Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $219.90   9.588%   $240.984   $240.98   $241.00   $241.00  
  Purchase #2 $51.70   8.514%   $56.1017   $56.10   $56.10   $56.10  
  Purchase #3 $12.70   12.478%   $14.2847   $14.28   $14.30   $14.30  
  Purchase #4 $25.53   9.106%   $27.8548   $27.85   $27.85   $27.90  
  Purchase #5 $16.53   4.862%   $17.3337   $17.33   $17.35   $17.30  
  Purchase #6 $182.53   13.841%   $207.794   $207.79   $207.80   $207.80  
  Purchase #7 $145.36   11.699%   $162.3657   $162.37   $162.35   $162.40  
  7 purchase totals = $654.25       $726.7186   $726.70   $726.75   $726.80